that the urea is in simple solution. This is presumed to be the case also with the pigment and extractives; but of these substances even less is known.

The uric and perhaps the hippuric acids are combined either with soda, potash, or lime, or with all three. Oxalic acid is probably at once combined with lime, and the salt is held in solution either by a combination of organic substance (mucus) or by the acid phosphate of soda, which exerts a slight solvent effect upon it (Neubauer). The chlorine is united in great measure to sodium; sometimes in part to potassium, especially when salts of potash are introduced largely with the food; the sulphuric acid is supposed to be combined chiefly with potash, and sometimes with soda and lime. The phosphoric acid is combined chiefly with soda in the form of phosphates, with one and two atoms of fixed base; but there are also phosphates of lime and magnesia (PO, + CaO + 2HO); (PO2+ 2CaO + HO) ; (PO + MgO + 2HO); and (PO5 + 2MgO + HO). It is probable that phosphoric acid is also in combination with potash; and sometimes, as an exceptional case, the whole of the phosphoric acid is combined with potash, and none with soda.1 Carbonic acid may be either free or combined with lime, as bicarbonate. Ammonia exists chiefly or entirely as chloride of ammonium, and perhaps sometimes as phosphate; and iron is either combined entirely with the pigment (Harley), or is united in part with chlorine (Bergman). The combinations of silicic, lactic, and other acids, when they exist, are not known.

The mode of combination of the acids and bases is extremely variable, being influenced, 1st, by the varying amounts of soda, potash, lime, and magnesia which enter the body with the food; and, 2d, by the varying amounts of sulphuric, phosphoric, and oxalic acids, which are formed by oxidation or cleavage in the body. There can evidently be no constant and immutable composition.

Altogether, the mean quantities of the ingredients enumerated in former pages, when added together, make up about 60 to 65 grammes 926 to 1003 grains in twenty-four hours, as the total amount of excretion.

In the following table the mean amounts of solids obtained by actual evaporation, by various observers, are given.

1 Thus, in Böcker's own urine the chlorine is united entirely to sodium; the phosphoric acid to potash (not to soda), lime (bibasic), and magnesia; the sulphuric acid to potash. The probable arrangement appeared to him: (CINa); (KaÓSO3); (2KaOPO); (KaOPO); (2CaOPO); (MgOPO). (Ueber die Wirkung des Biers. Archiv des Vereins, Band i, p. 347.)

Mean amount of urinary solids in twenty-four hours, as determined by evaporation and weighing :

In different individuals, the mean amount of solids may be from 40 to nearly 80 grammes, and the mean amount as fixed synthetically as well as experimentally may safely be put down as 60 grammes, or 926 grains, in 24 hours, in healthy men, on good diet, between twenty and forty years of age. The range in the same person is at least one third of the mean amount from day to day.

SECTION III.

ON THE AMOUNT OF EACH CONSTITUENT EXCRETED IN TWENTYFOUR HOURS BY A DEFINITE AMOUNT OF BODY WEIGHT.

The amount of urea excreted by one kilogramme of weight of the body is estimated, both by Professor Lehmann and Julius Vogel, at 0.500 grammes in twenty-four hours; this would give 3 grains to each 1 lb. avoirdupois. In nine men, aged from twenty-three to thirty-five, whose weights and true mean excretion of urea are known, I find the mean excretion of urea in twenty-four hours, to each kilogramme, to be as follows: 0.420; 0-424; 0.433; 0.449; 0·451; 0.457; 0.480; 0.483; 0.529 grammes, the mean of the whole is 0.459 grammes, or 3.36 grains, to each pound avoir.; the difference between the lowest and highest amount being 0.109 grammes, or about 20 per cent. All but one of these numbers are below those

1 Mean of sixteen days. Range from 424 to 882, or rather more than one third above and below the mean amount.

"A single day's observation. The amount is probably too high.

given by Lehmann and Vogel; but yet the difference is not material, and probably we shall be close to the truth in receiving 0.500 grammes as the mean excretion of urea for each kilogramme in twenty-four hours.

The weight of all the persons whose amounts of urea are tabulated in previous pages is not known; but as the mean amount of urea of all the cases is 33·18 grammes, it follows, if each kilogramme excretes 0·500 grammes, that the mean weight of all these men must have been 66 kilogrammes, or 145 lbs. avoirdupois. This is over the mean weight of men of this age in general; but it must be remembered that many of these persons were healthy, athletic, well-fed students, whose weights would be over the average. Adopting 66 kilogrammes, or 145 lbs. avoirdupois, as the mean weight of all the men whose urine has been analysed and recorded in former pages; and dividing the mean amounts of the urinary constituents before given, we get the following table:

Let us test these figures by the results obtained by others. We have already seen that the urea from the nine cases I have assembled is a little below the amount in the table (0.459 to 0-500), but the difference is immaterial.

The amount of uric acid in relation to weight is so variable in different persons, that I find the amount given in the table must be allowed wide limits of variation.

1 These numbers are probably incorrect; they are obtained by using Weissmann's imperfect analyses.

2 The amounts of creatin and creatinin are taken from Thudichum (mean in two men); but as the two men weighed not 66, but 70 and 72 kilogrammes, I have calculated the excretion upon the mean of these weights.

3 I have taken the chlorine at 7 grammes, or 108 grains. The amount of bases is so uncertain that I have not ventured to put in the figures.

Lehmann' says that one kilogramme in adults excretes, in twenty-four hours, 0.032 grammes of sulphuric acid. In two of my cases I found the amount 0.035 and 0.032 grammes, which is a little over the quantity given in the table.

The mean of the experiments of Hegar, Gruner, and Winter, give 0.064 grammes of phosphoric acid in twenty-four hours to each kilogramme, an amount which is over the quantity put down in the table. Some observations of Beneke's on himself, at different times, give the following numbers: 0.046; 0-039; 0.0427; 0.0426; 0.0315; the mean being 00403. This, on the other hand, is a little below the amount in the table.

It appears, therefore, clear that the amounts given in the table must be tolerably near the true quantities, and may be safely adopted.

The limits of variation above and below the mean excretion, according to weight, are certainly considerable. If we compare two persons, we find that one may excrete in twenty-four hours only 0.390 grammes (Beneke in one series), and another 0.529 grammes of urea to each kilogramme. And variations as great occur in the other ingredients. Also in the same person the amount of urea excreted by each lb. weight of the body at different times varies rather largely (even occasionally as much as 20 per cent.); so that certainly we must allow a wide range of mean maximum and minimum excretion, above and below the mean recorded in the table. In the other ingredients, the maximum and minimum excretion of each lb. weight is even greater than in the case of the urea.

SECTION IV.

ON THE AMOUNT OF THE ACIDITY OF THE URINE.

3

The acidity depends on a general excess of acids over alkalies; the immediate cause may be various, and may depend either entirely on acid phosphates (other acids, such as SO, hippuric and uric, being in large quantities) or, in addition, on the presence of an organic acids (lactic? butyric? valerianic?), or of some acid salt, other than the phosphate.

The amount of the acidity, as determined by careful neutralizing with soda,3 is often conveniently expressed by saying

1 Handbuch, 2d edit., 1859, p. 286.

2 The acidity should always be determined as soon after the urine is passed as possible, as it rapidly increases in most specimens of urine.

3 Archiv des Vereins, Band iii, p. 627.

(not that it is equal to so much alkali, but) that it is equal to so much crystallized oxalic acid. Reckoned in this way, the acidity in twenty-four hours in male adults is thus given by different observations :

The specific gravity of healthy urine has a mean of 1020, and ranges from 1012, or lower, to 1030 or higher. The variations depend especially on the varying amount of water, which causes the solids to be in relative greater or less quantity, and on the varying amount of solids. Of the various solids, the quantities, 1st, of the urea, 2d, of the pigment, 3d, of the chloride of sodium, and 4th, of the remaining constituents, must be supposed to be the most important. The specific gravity cannot point out which ingredient is affected, and great changes may occur in relative constitution without any alteration in the specific gravity. For example, the urea may be greatly increased, and yet, owing to lessening of the chloride of sodium, the specific gravity may be unaltered, &c., &c.

The rules for determining the solids by the specific gravity (multiplying the last two figures of the specific gravity by 2 for most cases, and by 2:33 for diabetic urine, which gives the amount in grammes in 1000 c. c.) give merely approximative results; yet, on account of the ease of determining the specific gravity, they are useful.

SECTION VI.

ON THE ORIGIN OF THE URINARY CONSTITUENTS.

1. In health, the water of the urine is derived entirely, or almost entirely, from the water of the liquid or solid food. Schmidt's experiments on cats show, however, that water is